1. Field of the Invention
The present invention relates generally to an improvement in an oscillating type of flow rate meter for use in a fluid supply system wherein the meter tends to fail to sense the real value of a flow rate of fluid fed to a fluid consuming means, because of a pulsation in the pressure of a pressurized fluid generated by a pump. More particularly the present invention relates to an improvement in an oscillating type of flow rate meter for use in a fuel consumption measuring system for a motor vehicle wherein meter tends to fail to sense the real value of a flow rate of fuel fed to the engine, due to a pulsation in fuel pump pressure of a pressurized fuel.
2. Description of the Prior Art
As is well known in the art, as an expedient forming part of a system for measuring fuel consumption of a motor vehicle such as an automobile, a fuel flow rate sensor is provided in a fuel passageway between a fuel pump and an air-fuel mixture forming device such as a carburetor all which form part of a fuel supply system for an engine of the motor vehicle. It is also known to provide the system with a vehicle speed sensor in addition to a fuel flow rate sensor so as to measures fuel consumption of the vehicle from input signals fed from the vehicle speed sensor and the fuel flow rate sensor.
As a fuel flow rate sensor employed in such a fuel consumption measuring system, an oscillating type of flow rate sensor or meter as shown in FIG. 1 of the accompanying drawings is known. As shown in FIG. 2 of the drawings, the flow rate sensor 10 is disposed in a fuel passageway 11 between a fuel pump (not shown) and an air-fuel mixture forming device which is a carburetor 12 in this example. As is shown in FIG. 1, the flow rate sensor 10 comprises a body or housing 13 formed with a chamber 14 partially having a generally cylindrical cross section. An inlet port 16 provides communication between the fuel pump and the chamber 14, and an outlet port 18 provides communication between the chamber 14 and a float chamber 19 of the carburetor 12. An oscillator 20 in the form of a pointed vane is pivotably mounted in the chamber 14 and extends from an upstream portion of the chamber 14 to a downstream portion thereof. A partition member 22 is arranged in the chamber 14 to be close to or to contact with the downstream end of the oscillator 20. The partition member 22 is spaced from a downstream internal wall surface of the chamber 14 to form therebetween a passage 23 which communicates with the outlet port 18. The partition member 22 has the cross section of an arcuate shape. The oscillator 20 is a pivoted vane which divides the chamber 14 at a location upstream from the partition member 22 into two sections 24 and 25. The partition member 22 defines a first outlet passage or nozzle 26 between one end thereof and an internal wall surface of the chamber 14 and a second outlet passageway nozzle 27 between the other end of the partition member 22 and an internal wall surface of the chamber 14. The first nozzle 26 provides communication between the section 24 and the passage 23 and the second nozzle 27 provides communication between the section 25 and the passage 23. The oscillator 20 is oscillated by fuel flow from the inlet port 16 into the chamber 14 so as to alternately engage an upstream end portion of the oscillator 20 with opposite upstream internal wall surfaces of the chamber 14 and to alternately communicate the inlet port 16 with the sections 24 and 25 to alternately pass a main flow of fuel fed into the inlet port 16 into the sections 24 and 25 of the chamber 14. When the upstream end portion of the oscillator 20 engages one of the upstream internal wall surfaces to pass a major portion or the main flow of fuel fed from the inlet port 16, into one of the sections 24 and 25, the oscillator 20 is urged and oscillated by the main fuel flow striking a downstream end portion of the oscillator 20, into a position in which the upstream end portion of the oscillator 20 is engaged with the other upstream internal wall surface of the chamber 14. This passes the main fuel flow from the inlet port 16 into the other one of the sections 24 and 25. By repeating such an operation, the oscillator 20 is alternately oscillated in opposite directions in the chamber 14 so that the main flow of fuel fed from the inlet port 16 is alternately passed from the nozzles 26 and 27 to the passage 23. Since the frequency of such an oscillation of the oscillator 20 is proportional to the fuel flow rate or representative of a function of the fuel flow rate, the fuel flow rate is measured by sensing the frequency of the oscillation of the oscillator 20. That is, when the flow rate is zero, the frequency of the oscillation produced in the flow rate sensor 10 is zero and as the flow rate is increased, the frequency of the oscillations produced in the flow rate sensor 10 is increased, for example, rectilinearly.
On the other hand, as the types of the fuel pump used in the fuel supply system for the engine, two types, that is, an electromagnetic type and a mechanical type are known. However, the two types of fuel pumps both generate pressurized fuel the pressure of which is alternately and repeatedly increased and reduced causing continuous periodic pressure pulsations as shown in FIG. 3 of the drawings. As a result, a pulsation of the pressure of fuel is produced in the fuel passageway 11 into which the pressurized fuel is fed from the fuel pump. When the pulsation of the fuel pressure is applied to the oscillating type flow rate sensor 10, the accuracy of measurement of flow rate by the flow rate sensor 10 is degraded to cause malfunction of the flow rate sensor 10. This is because, even when the supply of fuel from the air-fuel mixture forming device such as the carburetor to the engine is in fact zero and accordingly the frequency of oscillations in the flow rate sensor 10 is to be zero, a certain amount of fuel is passed through the flow rate sensor 10 by the pulsation of the fuel pressure to cause the oscillator 20 to oscillate with a frequency exceeding a value proportional to or representative of the flow rate of fuel fed to the engine which value is zero in this instance. As a result, the fuel consumption measuring system provides measurements representative of fuel consumption far higher than or inferior to an actual or real fuel consumption. Such a malfunction of the flow rate sensor 10, or such an influence of the pulsation of fuel pressure thereon, is especially conspicuous in engine operating range in which the speed of the vehicle is low and the flow rate of fuel fed to the engine is small. Also, the influence of the pulsation of fuel pressure on the flow rate sensor 10 becomes prominent when a fuel returning passage is provided between the fuel pump and the flow rate sensor 10, since the pulsation of fuel pressure is increased.
Various examples of the mechanism of the phenomenon of the flow rate sensor 10 being affected by the pulsation of fuel pressure are mentioned below.
1. Even if the amount of fuel fed from the carburetor to the engine is zero, a needle valve 28 is forced toward the interior of the float chamber 19 by the peak pressure of the pulsation above a predetermined valve. The needle value therefore assumes a position in which the peak pressure of the pulsation is balanced with a force urging the needle valve 28 in a direction to close an inlet port of the float chamber 19, as shown by the arrow in FIG. 2. As a result, when a certain amount of fuel flows into the float chamber 19 through the needle valve 28 to raise the level of fuel in the float chamber 19 from a normal or standard level t.sub.o to, for example, a level t.sub.x equal to or near the position or the height of the lower downstream edge of a main nozzle 29 by a value h, since the flow rate sensor 10 senses such a fuel flow, measurements indicate that fuel is consumed even though fuel is not in fact fed from the nozzle 29.
2. When a bubble of air in the fuel passageway 11 comes between the flow rate sensor 10 and the carburetor 12, it is compressed by the peak pressure of the pulsation of fuel pressure so that a certain amount of fuel flows through the flow rate sensor 10. That fuel flow is sensed by the flow rate sensor 10, and a measurement is displayed or obtained representing that the supply of fuel from the carburetor 12 to the engine is flowing even though the needle valve 28 is closed and fuel is not in fact fed from the nozzle 29.
3. When a pipe or hose forming the fuel passageway 11 between the flow rate sensor 10 and the carburetor 12 is expanded by the peak pressure of the pulsation of fuel pressure, due to a certain amount of fuel flowing through the flow rate sensor 10, the fuel consumption measuring system measures the fuel flow as if fuel is fed to the engine even though fuel is not in fact fed to the engine.